The present invention relates to a magnetic disk drive with a head gimbal assembly (HGA) including two or more types of control function units, and more particularly to a technique which is effective when applied to an HGA having a so-called two-stage actuator function and thermal asperity floating-control (TAF) slider function.
One proposed technique for precisely controlling the position of the magnetic head in a magnetic disk drive employs a two-stage actuator function to provide rough and fine head positioning movements in order to position the magnetic head at a desired location on the surface of the magnetic disk in a read/write operation (for example, see Japanese Patent Laid-Opens Nos. 2002-93086, 2002-74869, and 2000-357377). Briefly, in this technique, the magnetic head is driven by both a voice coil motor and the dimensional change of a piezoelectric element.
In order to improve the read/write characteristics of the magnetic head in this type of magnetic disk drive, another proposed technique employs a TAF slider function for controlling the flying height of the magnetic head above the magnetic disk surface (for example, see Japanese Patent Laid-Open No. 5-20635). Briefly, this technique forms a thin-film resistor together with a coil within the insulation layer enclosed by the lower and upper magnetic poles of the magnetic head, and causes the thin-film resistor to generate heat by passing a current through it. As a result, the end portion of the magnetic pole of the magnetic head protrudes, reducing the gap between the end portion of the magnetic pole and the surface of the magnetic disk.
The above techniques for magnetic disk drives employing a two-stage actuator function and a TAF slider function have the following problems. In the technique of above-mentioned Japanese Patent Laid-Open No. 5-20635, which employs a TAF slider function, for example, since the coil and the thin-film resistor are disposed close to each other, passing a current through the resistor to control it may affect the read/write characteristics of the magnetic head. Further, in recent years, there has been a need to carry out servo tracking at high speed with precision, as well as to lower and control the flying height of the head with precision in magnetic disk drives, requiring an HDA having a two-stage actuator function and a TAF slider function which match these controls.
Employing these two types of functions at the same time, however, may cause the following problems. Each of these functions requires a transmission line consisting of two conductors (for go and return currents) as control lines. Therefore, if these features are simply incorporated into the HDA without special arrangements, two control lines (each consisting of two conductors) must be installed in addition to the two transmission lines for the read/write signals of the magnetic head, totaling four transmission lines (8 conductors) to be disposed on the suspension.
The suspension, on the other hand, is designed to apply a load to float the slider. This load is set so that the flying height of the slider is precisely set to a target value. If, however, four transmission lines (8 conductors) are disposed, the total rigidity of the transmission lines increases, making it difficult to control the flying height using the load set for the suspension alone. Specifically, the rigidity of the transmission lines affects the spring load of the HGA and causes variations in the flying height, changing the flying characteristics, and hence the read/write characteristics of the magnetic head.